Inspection systems are widely known in which charged particles or electromagnetic waves are irradiated onto the inspection target, a secondary charged particle which is obtained according to the properties of a surface of an inspection target such as a semiconductor wafer or the like is detected by an imaging device by, whereby a pattern or the like which is formed on the surface of the inspection target is inspected by using image data generated based on the results of the detection (for example, Patent Literatures 1 to 3 below). As these inspection systems, in many cases, a system is adopted in which image data is generated by irradiating charged particles or electromagnetic waves onto an inspection target which is held on a movable stage while moving the movable stage and capturing a certain amount of light from the imaging device every time the movable stage moves a distance equal to one pixel of a imaging element. In this system, a TDI (Time Delay Integration) sensor is used as the imaging device. The TDI sensor has a plurality of imaging elements which are arranged in a predetermined number of stages in a vertical stage direction (which coincides with the moving direction of the movable stage). Amounts of secondary charged particles are integrated in the vertical stage direction in synchronism with the movement of the movable state (the inspection target) through the time delay integration, and an integrated detection amount of secondary charged particles is transferred every time the movable stage moves the distance equal to one pixel. According to the system, the amount of secondary charged particles is integrated by the predetermined number of stages, and therefore, when the inspection target is moved even in a high speed, it is possible for the system to have a high sensitivity for imaging. The TDI sensor is based on the premise that the movement of the movable stage and the transfer of secondary charged particles in the vertical stage direction are in synchronism with each other.
In the inspection process, it is desired that a defect is detected based on the generated image data, a type of the detected defect is determined, the defect whose type is determined is analyzed using an SEM (Scanning Electron Microscope) or the like, and the results of the analysis is fed back to the production process quickly. The defect's type determination step is a very important step since the subsequent analysis and feedback are dependent upon the results of the determination.
A luminance or shape which is specific to the type of a defect appears in an inspection image formed by the generated image data. Because of this, it is possible to determine a type of the defect based on the inspection image. For example, when a particle exists on an inspection target, an amount of secondary charged particles obtained from an area where the particle exists becomes larger than those obtained from other areas. Because of this, in the inspection image, a gradation value (a luminance value) of the particle existing area becomes higher than those of the peripheral areas and hence looks brighter. Due to this, the defect attributed to the particle is determined as a “white defect.” On the other hand, when a depression exists on the inspection target, an amount of secondary charged particles obtained from an area where the depression exists becomes smaller than those of other areas. Because of this, in the inspection image, a gradation value of the depression existing area becomes lower than those of the peripheral areas and hence looks darker. Due to this, the defect attributed to the depression is determined as a “black defect.”
Although the defect's type determination step can be executed by using software without involving manual work, there still exists room for improvement in accuracy. Because of this, normally, the defect's type determination is manually executed in many cases. In the manual defect's type determination step, normally, the operator determines on a type of a defect while looking at an inspection image, a reference image, a differential image and the like which are displayed on a review screen of an inspection system and inputs a classification code which corresponds to the results of the determination into a computer or the like. The reference image is an image that is supposed to be obtained when there is caused no defect in an inspection target. The differential image is an image that has, as gradation values, differences between gradation values of individual pixels of an inspection image and gradation values of corresponding individual pixels of a reference image.